The use of laser diodes has come in prominent use in optical disc storage units and optical telecommunications requiring long term reliability. One of the primary causes of laser diode failure in the field is low catastrophic optical damage (COD) levels due to enhanced light absorption at the facet or defect creation and migration at the laser facet surface. The general treatment in the past has been to utilize III-V materials at the facet surface which are lattice matched with the internal crystal structure and have a wider bandgap than the active layer. As an example, in U.S. Pat. No. 5,491,711, there is disclosed an InGaAs/GaAs active region with a thin facet layer of aluminum or phosphorus that converts the near-surface material to a wider bandgap. Another example is U.S. Pat. No. 5,228,047 disclosing a facet window structure comprising AlGaAs or InGaAlP or their combination having a sufficient thickness of 0.2 nm to 3 .mu.m to prevent local generation of crystal defects by lattice mismatching between the window layer and the laser device. Further, a protective layer may be formed over the window layer having a bandgap different from that of the window layer. U.S. Pat. No. 5,228,047 teaches the use of a sulfur-containing layer on the facet as a protection layer.
The teaching of the use of sulfur-containing materials to passivate and protect the laser facet has become prevalent. In U.S. Pat. No. 5,260,231 and 5,208,468, a sulfur-containing film is formed with a sulfur-containing solution, e.g., undiluted (NH.sub.4).sub.2 S solutions, aqueous (NH.sub.4).sub.2 S solutions, undiluted (NH.sub.4).sub.2 S.sub.x solutions or aqueous (NH.sub.4).sub.2 S.sub.x solutions, on the facet surface of an AlGaAs semiconductor laser to remove surface oxygen, followed by the electron beam evaporation of a protective film, such as Si.sub.3 N.sub.4, AlN, C, MgF.sub.2, CaF.sub.2, NaF, ZnS or ZnSe. Other examples are U.S. Pat. No. 5,451,542 relating to a photosulfidation process using ultraviolet light and sulfur vapor to remove native oxide from a III-V surface. U.S. Pat. No. 4,751,200 passivates a III-V surface to reduce surface recombination velocity using a spin-on solution of sodium sulfide. U.S. Pat. No. 5,300,320 passivates III-V substrate surfaces using a MOCVD precursor to form a film where the precursor is a butyl group plus GaS or AlS or GaSe or GaTe. U.S. Pat. No. 5,116,767 teaches the deposit of sulfide films on InGaAsP lasers to passivate defects on the laser facets.
U.S. Pat. No. 4,811,077 discloses the passivation relative to the improvement of surface carrier recombination at III-V compound semiconductor surfaces using a combination of very thin layers. In the preferred embodiment, a pinning control monolayer (i.e., prevention of pinning or unpinning of the Fermi level) of GaS is deposited, followed by a 1 nm to 1,000 nm dielectric, ambient inert, dielectric, translucent protective layer of SiO.sub.2 deposited by PECVD, although other deposited protective layers are suggested, such as CaF.sub.2, NaS, ZnS, GaP, GaSe and polyimides. However, nothing is disclosed or taught as to how these layers may affect optical properties or relate to facet preservation or how they may be applied in the presence of previously deposited metal layers.
It is, therefore, an object of this invention to provide an optical semiconductor device with improved reliability.
It is another object of this invention to provide improved surface passivation of an optical semiconductor device with decreased surface recombination velocity.
Another object of this invention is to provide semiconductor laser diode devices that have a higher catastrophic optical damage level compared to prior semiconductor laser diode devices.